On home soil, which has historically been a fortress for the red and blacks, the Crusaders couldn't get any flow to their play as the Highlanders produced some stifling defence and were clinical on attack.
Speaking after the match, Robertson said the error count told the tale of how his side had performed.
"We made 22 errors; I think 15 handling errors and we turned a bit of ball over at the breakdown," he said.
"Their urgency and desperation was pretty exceptional. We missed a couple of early calls at scrums and lineouts, they did a really good job on us. We'd planned for it, but they still executed and we couldn't counter it. You're just sitting in the box thinking how we could be smarter here...it was a different feeling.
"Effort was high for us, but our accuracy was poor. Oh well, it's good for the comp; it's livened things up anyway."
Heading into the game, the Crusaders were the sole unbeaten team in the competition, winning their first four games by an average of 17 points, and appeared to be cruising toward the final.
The Highlanders stopped that narrative dead in its tracks, however, with one of the more memorable wins in recent history for the club.
Connor Garden-Bachop making a try in the tackle of David Havii. Photo / Photosport
While the result and just how dominant a performance it was from the Highlanders surprised many, a pair of former Crusaders were among those to step up against the reigning champions.
First five-eighth Mitchell Hunt and loose forward Billy Harmon, who joined the Highlanders this year after being unable to secure a contract with the Crusaders, both had strong outings and Robertson praised their play after the match.
"If we could have kept Billy we would have," Robertson admitted of Harmon. "It was just the model of the structure in our contracting. He was exceptional. He is a great player and I'm stoked for him.
"They performed like we know they can and have done so for us over the years, so well done to them," he added.
